Implantable medical devices (IMDs) variously provide physiological data monitoring and therapy delivery, including cardiac defibrillation, pacing, and resynchronization therapy. Fully implanted IMDs function autonomously through preprogrammed control and often record patient physiometric information. The physiometry, as well as parametric data, can be respectively retrieved and downloaded by interfacing the IMD to programmers, repeaters, and similar external devices, which program, troubleshoot, and exchange the physiometry and parametric data through induction, radio frequency, or other wireless telemetry. Programmers are full-function interrogators designed for clinical use with a range of IMDs. In contrast, repeaters are limited-function interrogators, which are often matched to a specific IMD and are intended for remote at-home patient use.
Cardiac rhythm management (CRM) devices are a particular form of IMD, which provide therapeutic electrical stimuli to the heart in response to cardiac arrhythmias. Pacemakers, for instance, manage bradycardia, which is an abnormally slow or irregular heartbeat, by delivering pacing stimuli to restore normal sinus rhythm through electrodes provided on stimulation leads, such as endocardial or epicardial pacing leads. Implantable cardioverter defibrillators (ICDs) treat tachycardia, which are abnormally fast and life threatening heart rhythms, through high energy cardioversion, defibrillation shocks, or anti-tachycardia pacing. CRM devices also continually monitor and record patient physiometry and parametric data on therapy delivery, which are retrievable by caregivers through device interrogation.
Conventional arrhythmia management using CRM devices is episode-focused. Changes in heart rhythm are monitored by a CRM device as arrhythmic episodes potentially requiring therapy to convert, mitigate, or interrupt the change. When the magnitude or duration of an episode exceeds a fixed threshold, therapy may be delivered by the device. Arrhythmic episodes of duration shorter than the threshold are not considered actionable, even though of clinical importance to providing overall arrhythmia management.
The focus on episodes is dictated to some extent by device limitations. CRM devices are intended for long term implantation, yet have limited battery life and finite data storage capacity. Increasing discrimination over the selection of actionable episodes, such as through tiered therapy, preserves battery life and avoids patient discomfort from unnecessary treatments. Similarly, storing only those episodes that resulted in therapy delivery, plus a limited set of other non-actionable episodes, can conserve data storage. When no data storage remains, the oldest episodes are discarded to free storage space. As a result, the longer the time between CRM device interrogations, the more episodes may get discarded.
U.S. Pat. No. 7,265,676, issued Sep. 4, 2007 to Gordon et al., describes an alert system and method for an IMD, which detects the occurrence of an event for clinician attention. The IMD alerts on therapy delivery, arrhythmias, heart failure, system integrity, and cardiac ischemia events. The arrhythmic events include atrial and ventricular fibrillation, including non-sustained tachycardia. Cardiac signals are analyzed against an alert criterion before generating an alert from the IMD to patient or clinician. However, alert generation is limited to arrhythmic episodes identified in on-device data only.
Therefore, an approach is needed to provide identification of potentially arrhythmic conditions based on expanded device-originated physiometry and parametric data without excessive depletion of device resources.